1. Field of Invention
The present invention relates a method of producing hydrogen storage alloy to be served in such as material for hydrogen storage and supply, material of absorbing hydrogen for heat exchange, material for supplying hydrogen for fuel cell, material for negative electrode for Ni-hydrogen cell, material for refining and recovering hydrogen, or material of absorbing hydrogen for hydrogen gas actuator.
2. Related Art
Conventionally, there has been a compressed gas system or liquid hydrogen system as an instrument for storing and transporting hydrogen, and now in place of these practices, a system using hydrogen storage alloy has been noticed. As known, the hydrogen storage alloy has a property reversely reacting with hydrogen, absorbing and desorbing hydrogen simultaneously with xe2x80x9cin and outxe2x80x9d of heat of reaction. It has been attempted to proceed to practice a technique making use of this chemical reaction for storing and transporting hydrogen, and it has been progressing to develop and practice a technique utilizing heat of reaction for structuring the heat storing and transporting system. Aiming to practicing these attempts, many kinds of hydrogen storage alloys have been developed, and representative hydrogen storage alloys are knows as LaNi5, TiFe, or TiMn1.5.
Incidentally, for proceeding various kind of usage to practice, it is necessary to more improve characteristics of materials for storing hydrogen, and big problems involved are to increase an amount of storing hydrogen, cost down raw materials, and improve a plateau property or durability endurance.
Among the above mentioned representative hydrogen storage alloys, TiMn based alloy is large in a maximum amount of occluding hydrogen and preferable in the plateau property, and being very excellent in endurance depending on a composition, it is one alloy system of this kind expected toward practicing. However, also in this alloy, since a plateau and hysteresis factor is large and rechargeable hydrogen capacity is small, a sufficient performance cannot be effected when practicing, and it is therefore difficult to apply this alloy to a severe system in a pressure range such as a heat pump. There has been known a method of reducing an xcex1 phase area at an initial hydrogenation by replacing a part of Ti with V so as to increase rechargeable hydrogen capacity, but it has not yet reached a practicing level. JP-A-7-102339 proposes an alloy where one part of Ti of TiMnV based alloy is replaced with Zr, thereby to increase the maximum amount of absorbing hydrogen while reducing a soluble area, and largely increase rechargeable hydrogen capacity. However, since the substitution of Zr increases a slope of the plateau as substituting the amount of Zr, such a proposed alloy cannot be applied as it is to the system, and a very small amount of adding Zr is possible (1.7% in terms of the ratio of the atomic amount).
The invention has been realized in view of the above mentioned circumstances, and it is an object of the invention to provide a method of a practical hydrogen storage alloy which enables to effectively absorb and release hydrogen at room temperatures, shows an excellent maximum hydrogen capacity and rechargeable hydrogen capacity in comparison with conventional materials, exhibits a superior plateau and hysteresis property, and has an excellent characteristic especially near the room temperatures.
For solving the above mentioned problems, a first invention of the method of producing the hydrogen storage alloy, which is expressed with a formula of TiaMnbVcZrdAeBfCgNih, a crystal structure of which comprises a hexagonal close-packed structure, characterized in that a molten raw material is rapidly solidified for obtaining the hydrogen storage alloy, herein, a is 10 to 40 atomic %, b is 40 to 60 atomic %, c is 5 to 30 atomic %, d is 15 atomic % or less, e, f, g, h, e+f+g+h are 0 to 10 atomic %,
A: one or two kinds of Fe and Co
B: one or two kinds or more of Cu, Zn and Ca
C: one or two kinds of Al and Mo.
A second invention of the method of producing the hydrogen storage alloy as set forth in the first invention is characterized in that the molten raw material is rapidly solidified to be a final alloy without carrying out a homogenization treatment.
A third invention of the method of producing the hydrogen storage alloy as set forth in the first or second invention is characterized in that a cooling rate at a rapid solidification is 103xc2x0 C./sec or higher.